The true extent of the world's mangrove forests has been mapped for the first time ever with new satellite data. The picture revealed is an alarming one.

The new satellite images show that mangrove forests are far smaller than previously thought and that they are disappearing at a pace that outstrips other threatened ecosystems.

The map made from the satellite data shows that approximately 53,190 square miles (137,760 square kilometers) of mangroves exist on Earth's surface. That's about 12 percent lower than earlier estimates.

"This reveals that 75 percent of the forest is found in just 15 countries, out of which only about 6.9 percent is protected under the existing protected areas network," said study researcher Chandra Giri, of the U.S. Geological Survey.

Mangrove forests grow in tropical and subtropical tidal zones, and they are among the most productive and biologically important ecosystems on the planet. The trees, palms and shrubs of these forests have adapted to the most severe environmental conditions, thriving in regions of high salinity (salt concentration), scorching temperatures and extreme tides along the equator.

However, human activity and frequent severe storms have taken their toll, resulting in a loss rate formangrove forests higher than the loss of inland tropical forests and coral reefs.

"The current estimate of mangrove forests of the world is less than half what it once was, and much of that is in a degraded condition," Giri said.